How to include file bytes into the POST request body in Jmeter? (What encoding to use) - rest

Question

I have to perform POST requests from Jmeter. I use default HTTPRequest sampler, where I specify the JSON structure that is understandable by the testing app. One part of this JSON has to contain binary data from a pdf file.
For reading the file I use BeanShellSampler in the setUp thread group:
File file = new File(bsh.args[0]);
try {
FileInputStream fis = new FileInputStream(file);
byte[] array = new byte[(int)file.length()];
log.info("String is read.");
fis.read(array);
vars.put("fileEntity", new String(array, "cp1252"));
} catch (e) {
e.printStackTrace();
log.error(e.getMessage());
}
The problem is that when I look at the request with Fiddler, I see that difference, how the binary object is represented there in comparison with Postman's requests:
Postman
Jmeter
I think that there is something wrong with the encoding when I create a String object in the BeanShellSampler. What encoding is correct?
I tried to use RawDataSource plugin but it doesn't help for two reasons:
It fails to read my file, saying "Error reading next chunk"
It uses the same approach that I do to read the file, but uses UTF8 encoding. I tried this encoding also, but without any success.

Answer 1

My expectation is that your fis.read(array); function relies on default value of the file.encoding system property which may or may not be cp1252.
I would recommend introducing an InputStreamReader and explicitly specify the encoding there like:
InputStreamReader isr = new InputStreamReader(fis,"cp1252");
Also be aware that starting from JMeter 3.1 it's recommended to use JSR223 Test Elements and Groovy language for scripting mainly because Groovy performs much better comparing to Beanshell.